1. Statement of the Technical Field
The inventive arrangements relate to transceivers. More particularly, the inventive arrangements relate to a switch circuit for connecting a transmitter or a receiver to an antenna.
2. Description of the Related Art
Conventional RF power amplifiers commonly make use of one or more RF power dividers and combiners. These RF dividers and combiners are conventionally used to distribute RF power to a plurality of RF power amplifier circuits for amplifying an RF signal. The output RF signals from the plurality of RF power amplifier circuits are subsequently combined in one or more combiner circuits to form a single high power RF output. A quadrature (90°) hybrid coupler is commonly used to implement an RF power divider. The same type of quadrature (90°) hybrid coupler can also be used to implement an RF power combiner.
A conventional transceiver circuit 100 including the above listed components is shown in FIG. 1. With regard to FIG. 1, a first quadrature (90°) hybrid coupler 106 is provided with an input port 154, an isolated port 150, and output ports 152, 156. The input port 154 is coupled to a transmitter 102. The isolated port 150 is coupled to ground through a resistive termination 104 (for example, a fifty ohm resistor). Each output port 152, 156 provides an output RF power that is reduced by half relative to the RF power at the input port 154. However, the RF signal provided at output port 152 is 90° out of phase relative to the RF signal at output port 156. Quadrature hybrid couplers of this type are well known in the art. The output port 152 is coupled to a first power amplifier 108. Likewise, the output port 156 is coupled to a second power amplifier 110.
The transmitter 102 can communicate a radio frequency (RF) signal to the first quadrature (90°) hybrid coupler 106. Subsequently, the quadrature (90°) hybrid coupler 106 communicates a first output RF signal to the first power amplifier 108 and a second output RF signal to the second power amplifier 110. Each power amplifier 108, 110 performs actions to amplify the received RF signal's power by a certain amount. Thereafter, these power amplifiers 108, 110 communicate the amplified RF signals to input ports 160, 164 of a second quadrature (90°) hybrid coupler 112. This second quadrature (90°) hybrid coupler 112 is implemented in a reverse arrangement within the transceiver circuit 100 as compared to the first quadrature (90°) hybrid coupler 106. In effect, the second quadrature (90°) hybrid coupler 112 acts as a combiner, i.e., combines the amplified RF signals. However, those skilled in the art will appreciate that signals received at input port 160 will be phase shifted by 90° relative to signals received at input port 164. In effect, the phase shift at ports 160, 164 is opposite the phase shift at ports 152, 156 so that the net result is that the signals received at ports 160 and 164 are combined in phase at the output port 162. After combining the two amplified RF signals, the quadrature (90°) hybrid coupler 112 communicates the resulting RF signal along an electrical path to the antenna 116. This electrical path is typically comprised of an antenna switch 114. For example, the antenna switch 114 can be implemented using PIN diodes. The PIN diodes in the antenna switch 114 are controlled by a high voltage/high current control signal provided by a DC power source 120. In a transmit mode, the antenna switch 114 creates a low loss path between an output port 162 of the second quadrature (90°) hybrid coupler 112 and the antenna 116.
In receive mode, the antenna switch 114 disconnects the quadrature (90°) hybrid coupler 112 from the antenna 116 and instead creates a low loss path between the antenna 116 and a low noise amplifier 122. Consequently, a received radio frequency (RF) signal is communicated from the antenna 116 to the low noise amplifier 122 through the antenna switch 114. The low noise amplifier 122 performs actions to amplify a received RF signal's power. Subsequently, the low noise amplifier 122 communicates the amplified RF signal to a receiver 124.
Despite the advantages of this conventional transceiver circuit 100, it suffers from certain drawbacks. For example, the antenna switch 114 can introduce significant amounts of loss into the transmit path. This loss requires the power amplifiers 108, 110 to produce additional RF power output in order to achieve desired RF power output at the antenna 116. In turn, the additional RF power required from the RF power amplifiers 108, 110 requires more power from an external power supply (not shown). Consequently, the overall efficiency of transceiver circuit 100 is reduced. In addition, the antenna switch 114 is often comprised of a PIN diode RF switch designed for handling substantial levels of RF power. Such an antenna switch 114 often requires hundreds of volts to operate. Notably current power supplies that are suitable to provide such a voltage to the antenna switch 114 are difficult to incorporate into portable equipment.
In view of the foregoing, there remains a need for a transceiver circuit having an antenna switch circuit that can minimize the amount of power loss experienced by a transmitted RF signal. There also remains a need for a transceiver circuit having an antenna switch circuit that requires a lower voltage to operate.